Method of extracting gallium oxide from aluminous substances



N0v.6, 1951 M, BEM' f 2,574,008

METHOD OF' EXTRACTING GALLIUM OXID FROM ALUMINous sUBsTANcEs Filed Deo.2o, 1947 MMM) ff?, INVENTOR ww/7, M *faul ATTORNEYS Patented Nov. 6,1951 METHOD F EXTRACTING GALLIUM OXIDE FROM ALUBIINOUS SUBSTANCESMaurice Beja, Paris, France, assignor to Pechiney Compagnie de ProduitsChimiques et Electrometallurgiques, Paris, France, a corporation of theFrench Republic Application December 20, 1947, Serial No. 792,947 InFrance December 30, 1946 11 Claims.

The object of this invention is to separate and recover gallium fromaluminous materials wherein gallium is present in very small quantitles.

Aluminum ores invariably contain small quantities of gallium, In Frenchbauxite, for example, there are about 0.02 to 0.05 parts of GazOa forevery 100 parts of AlzOa. Industrially, alumina is generally obtainedfrom bauxite by a method known as the Bayer Process for the Purificationof Bauxite, or simply the Bayer Decomposition. In that process, the oreis rst digested with a solution of caustic soda; and after the insolubleimpurities have been removed from the liquor, the latter is seeded withaluminum hydroxid crystals as a primer to precipitate and recover about60% of its aluminum content as substantially pure `aluminum hydroxid. Byusing the decomposed aluminate liquor left after removing theprecipitate, to digest more of the ore and repeating the aforesaidsteps, the operation may be continuous or cyclic as generally practicedin Bayer plants.

Since the decomposed aluminate liquor in a Bayer plant containsrelatively small amounts l of sodium gallate, that liquor may be used asa source material for the recovery of gallium by treating it by themethod of the present invention. The latter is based upon the fact thatalumina and gallium oxid are both amphoterlc with the gallium oxidslightly the more acidic, wherefore, as I have found, the very slightdifference in their behaviour due to this may be utilized to effect theseparation of the greater part of the gallium oxid from the alumina. Itis to be understood that the decomposed liquors in a Bayer plant are notthe only source of material which may be treated by this invention; forany similar liquor containing Ga203 and A1203 is, of course, susceptibleto this treat ment, as well as any fresh liquors derived by dissolvingaluminous substances in an alkaline solution.

To illustrate, by way of example, suitable procedures for practicing thepresent invention, Flow Sheets l and 2 have been provided in theaccompanying drawings.

In describing this invention, it will be assumed, for example, that thestarting or source material is an aluminous substance such as bauxite,and that the latter is rst digested with a caustic soda solution todissolve its alumina and gallium oxid content. After removing anyinsoluble impurities from the liquor (which,

2 as in the Bayer Process, now comprises a caustic solution of sodiumaluminate and sodium gal-V late) the liquor, may be treated to slowlyprecipitate a portion of its sodium aluminate as substantially purealuminum hydroxid which,

late as compared with its concentration in the initial caustic solution.By slow precipitation, wherever referred to herein, is meant aprecipitation of the order of that in the Bayer Process wherebysubstantially pure aluminum hydroxid is thrown down and the sodiumgallate left sub-,V Y stantially undisturbed in the liquor.

Such a result, as will be readily understood, cannot be attained unlessthe liquor is treated very slowly and gradually.

The aforesaid precipitation of the substantially pure aluminum hydroxidfrom the aluminate liquor may be effected in different ways, butpreferably by neutralizing slowly the excess NazO of the liquor bythegradual addition thereto of an acid. For this purpose carbonio acid gasmay be caused to bubble slowly through the liquor. While carbonio acidis preferred, any acid whatever may be used for this purpose. Anotherway of precipitating substantially pure aluminum hydroxid from thealuminate liquor is to subject the liquor to spontaneous decompositionin the presence of an alumina primer, such as crystals or seeds ofaluminum hydroxid. In fact, if the liquor is unstable at the temperatureof processing, a slow hydrolysis will normally occur accompanied by the4precipitation of aluminum hydroxide. Such instability depends upon theratio of NazO to A1203 in the aluminate liquor and also upon itsconcentration; and, as in the case of a Bayer Decomposition, theintroduction of an alumina primer into an unstable aluminate liquorpromotes hydrolysis.v

While the precipitate produced in a Bayer Decomposition contains verylittle gallium, the

Bayer Process, as generally practiced under industrial conditions, doesnot permit the separa-I tion and recovery from the liquor of more thanits ratio in the ore treated. However, since in the Bayer Process whenoperated continuously, the stable decomposed :aluminate liquor isreturned to react with a fresh quantity c'ffzthe ore (the addition ofwhich makes the liquor unstable again), the repeated recycling oftheliquor builds up said ratio untillinihelng it becomes stabilized atabout to 20 times the ratio of Ga2O3 to AlzOain the ore treated.Consequently, these cycled aluminateiiquors of the Bayer Processconstitute an excellentjraw material for the recovery of galliuminaccordance with the present invention; for by taking these stableliquors, in Whichtheratio'of `Gra203 to `A1203 vmay .already .have 4beenincreased to 15 or ,20 times theirratio intheore, .and slowly treatingthem .with van ,.acid, as previously ex plained, the molecular .ratio of,NazO to A1203 will loe loweredlsufficien-tly .to make them unstable andthereby .-bring .about further .decomposition byhydrolysis. and .hencefurther precipitation ..of pure .aluminium hydroxid. Thus by continued.or repeated. .slow .neutralization of precipitation of aluminumhydroxid. .Such intheNazO, the concentration of .Ga203 in these liquors.may .be .increased to many .times its concentration in a Bayer plant,.before recovering the .Ga203 .as .aforesaid .with .the Alast .fractionof the alumina.

The followingexamplesare illustrative of the procedural Ysteps .whichmay be .used -in Vpracticing the invention,

Example 'f1 It willbe assumed that, vbvreactingan aluminous substancewithpaustic soda, .an aluminate solution or `liquorhas Abeen .obtainedcontaining,T

100 gm.,N,a2,0 per. liter .and Jhaving .the following relative molecularcomposition:

4 A1203 :for .20 NazO that is, a ratio of 1 to 5 at which the liquor isstable since at this-ratio lthe A1203 and NazO are closeto being 'inequilibrium at the concentration and `temperature specified. The liquoris now slowly `and partially carbonated 'by bubbling CO2 gas through ituntil the ratio Vbecomes 4.A12O3 .for 5 Naz() that is, a ratio of 4 to`5 at Which'the liquor is unstable again so Lthat a vfurther `'BayerDecomposition may 'be used to precipitate and remove additional aluminafrom the liquor and reduce the'ratio to that is, aratio .of 1 to 5againvvhere the liquor, after theremoval o f the precipitate,Y is yoncemore stable but contains only le of its original alumina together withall or substantially all of its original GazOx. The liquor is nowtreated with CO2 gas again, but this time rapidly and sufficiently toprecipitate all its remaining alumina vtogether .with all ofits GazOs.'f Inthis nal precipitate,

which, as will be noted,'is obtained by complete .carbonation of theliquor, the ratio of GazOa to A1203 is ten times greater than intheoriginal 'aluminate solution.

A'lf the original aluminate liquor in Example l4 had been taken from therecycled liquors of a *Bayer plant, it is obvious that the finalprecipitate obtained by complete carbonation would have contained .150170.200 times more GazOa in relation to its alumina content, thanexisted in the `bauxite treated; wherefore by processing such -recycledfliquors in accordance with the procedure `in .Example l, it is possibleto obtain an alumina, at the end of complete carbonation, containing atleast .3 .parts-.of GazOs for every 1.00; parts of alumina, Whereas .theVbauxite treated contained only 0.02.par.ts,of Gaz03 for every .100parts of alumina.

It .will be understood .that the ,terms stable and unstable Whereverthey appear in the specification and claims .hereof `are to beconstruedas explained above inExampleLand that the nouns stabili-ty-andfinstability .Wherever they appear in the specification and claims eachdenotes respectively the .condition defined .by the correspondingadjectives .stableor unstable as the case may be.

Example-'2 A batch of stable `sodium, aluminate liquor obtained from a.single Bayer Decomposition and having, as in Example 1, theratio of 4Al203 to 20 NazO (i. e. `1 to .5) l,is .partially carbonated bytreatment .with .CO2 .until .say about 1%; of its alumina is`precipitated along with an appreciable quantity of Ga203. This.precipitate is .removed .and dissolved in ,a .fresh `batch of 4the`aforesaid aluminate liquor, thus rendering thiszliquor unstable. .Thisunstable liquor is ,now subjected to a single Bayer Decomposition toprecipitate valuminum .hydroxid Witha little or nohgalliumhydroxidVthereby reducing itsAlzOs .to :NazO ratio to .the .stable ratioof 41 .to 5 or thereabout and' the liquor remaining, after removal-ofthis precipitate, Ais also subjected to xthe'aforesaid partialcarbonation whereby, say%ofrits aluminum content together with a littleof its v`gallium content can be-removed and which may be, as in the casebefore, dissolved in a fresh batch of 4the stable aluminate liquor; andthen the same steps which followed the 'removalzof -the rst 1260i thealumina, are repeated. .By proceedingin this manner, the operation mayb'e :continuous or cyclic Ias illustrated inFlowSheet 1. The liquor leftafter each partial carbonation `and removal of the precipitate so formedis, as'rshown in Flow Sheet 1, iinallyzand completely 4carbonated Vtoremove all its contained Ga203 and remaining alumina together.. ItLvvill be :noted that, in this example, vthe alumina` remainingdissolved inthe liquor after each partial carbonation'is proportionatelyabout 116 less than `that left dissolved in the liquor after thev:partial carbonation in Example 1.

It is obviousthat-if, .in Example 2, the initial liquor has been takenfrom therecycled liquors of a Bayer plant instead-of, as inthe caseassumed, .from a Bayer liquor-which had Vbeen subjected -to onlyasing-le .Bayer Decomposition, the

Ga203 present in the precipitate obtained r'at the end by'co'mpletecarbonation, would have been upwards of 7.5% of the aluminain'thatprecipitate. Moreover, it is possible to obtain an ultimateprecipitate still richer in Ga203, by dissolving'the 3% Ga20aprecipitate obtainable bythe procedure of Example .1, or the 7.5% Ga203precipitate obtainable by the procedure of Example 2,*in a caustic sodasolution and then treating the resulting liquor in accordance with theIprocedure of Example 2.' In such casesan ultimate precipitate could beobtained containing upwards of'=10 parts of Ga203'for every'lOO parts ofalumina; and since in these cases the alumina'remo'ved after each BayerDecomposition would itself 'be fairly rich in Ga203, .the same shouldnotbe discarded' but retained' and dissolved 'inf'that' fraction of thedecomposed aluminate liquor cyclingin the Bayer Process which isintended fora sub--l sequent operation to extract Ga203.

Example 3 -In 'this example, as in Example 2, say 1% of the alumina,together with an appreciable amount of Ga203, are precipitated from astable aluminate liquor by a partial carbonation thereof and theprecipitate withdrawn and redissolved in a fresh batch of the liquorthereby rendering the latter unstable. But instead of vsubjecting thisunstable liquor to a Bayer Decomposition, asA in Example2, it issubjected to a slow partial carbonation to precipitate substantiallypure aluminum hydroxidv and then, after this precipitate has beenremoved, the 'remaining liquoris" Vsubjected to a complete carbonation,as in Example 2.' yThe procedure here may also be continuous or cyclicas illustrated in Flow Sheet 2. Moreover, it will be obvious that inthis procedure it may be desirable that a Bayer Decomposition be used toremove substantially pure alumina directly preceding one or more of thepartial carbonation steps.

Besides being admirably adapted to the recovery of the gallium contentof Bayer liquors, the method of this invention is also particularlysuited for the recovery of the gallium oxid contained in the anode metalof aluminum rening tanks where, by the known electrolytic process of thethree melted layers, the lighter rened metal forms the upper layer, andthe raw metal the lower layer with the electrolyte layer lying betweenthem. During the electrolytic process, part of the aluminum istransferred from anodic layer into cathodic layer and the impurities,including gallium, in the anode metal builds up. When the quantity ofimpurities contained in the anodic metal has become too high, part ofthe anodic metal is removed and replaced by commercial aluminum. Theanodic metal so withdrawn contains, besides various impurities which arepresent in small quantities, about 60% of aluminum, of copper and 0.2 to0.7% of gallium. By reacting this withdrawn anodic metal with causticsoda or with a decomposed aluminate liquor from the cycle of a Bayerplant, all of the aluminum and gallium passes into solution; and afterseparating and removing the copper and the impurities which haveremained insoluble, the dlear aluminate liquor may be processed inaccordance with the present invention to yrecover its gallium content.

When aluminous material, either in ore, anodic 6. ing aluminate liquoris "too high'to permit a Bayer Decomposition. In such a case thesolution, as will be understood, must be rst rendered unstable byneutralizing part of the caustic soda with an acid and preferably C02.

Instead of completely dissolving in caustic soda the alumina from whichit is desired to extract the gallium, a smaller quantity of soda may beused and the reaction effected under pressure. Thus,lby treating, forexample, in'an autoclave at about-.160 0,1250 gm. of A1203 (in the formof the hydroxid, fAl20a.3I-I20) with 1 litre of analuminatetsolutioncontaining 200 gm. of caustic Na20 and 120 gm. ofA1203 per litre, all the gallium oxid is'dissolved from the aluminatreated,

whereas only about gm. of alumina gointo solution. The undissolved gm.of A1203 remain in the form ofthe hydroxid Al2O3H20 which is practicallyfree fromjgallium.

The separation or extraction of the gallium solves in the organicsolvent, while the alumina' remains in the aqueous solution. However,when the ratio of the galliumto aluminum content of the ultimateprecipitate is so high as to approach the order of 10 parts o'f- 1Ga203to 100 parts of Al203,"treatment.of the precipitate with an acid, whiledissolving'all of the A1203, leaves very sub-IV stantial portions f YtheGazOs undissolved by thek acid and which thereforeremain in the in"soluble residue. Such residues'have been obtained containing 20 to 30%Ga203. The relatively small quantity of Ga203 which passes into acidsolution in any such case can be precipitated by hydrolysis of thesolution, if necessary, after rendering it basic.

I claim as my invention:

1. Given a caustic alkali solution of aluminous material containing asmall amount of gallium and of sufficiently high concentration in A1203to be unstable, the method of separating and recovering the galliumcontent thereof which comprises rst precipitating by hydrolysis andremoving from the solution substantially pure aluminum hydroxid toreduce its concentration in A1203, partially neutralizing the solutionby an acid added thereto in small increments to slowly precipitatefurther aluminum hydroxid, removing this second precipitate from thesolution, thereafter acidifying the solution sufficiently to causesubstantially all of the aluminum and gallium content remaining in thesolution to precipitate together as hydroxids, removing the latterhydroxids and treating them to recover their gallium content.

2. The method of claim 1 further characterized by this: that suiiicientaluminum hydroxid is removed in the first step to reduce theconcentration of A1203 in the solution to the point where the solutionis stable.

3. The method of claim 1 in which the step of partially neutralizing thesolution is effected by bubbling C02 gas through the solution.

4. Given a caustic alkali solution of aluminous material containing asmall amount of gallium and of sumciently low concentration in A1203 tobe stable, the method of separating and recovering the gallium contentthereof which comprises partially v`neutralizing the solution by an acidAadded thereto in. small increments to. slowlr precipitate substantiallyV,pure aluminum. hy'- droxid, removing the precipitate from thesolution, thereafter acidifying the vsolution sufficiently to causesubstantially lall ofthe remaining laluminum and gallium content toprecipitate together as hydroxids, removing the latter hydroxids andtreating them to recover their gallium content.

5. The method of claim 4- in which the step o'f partially neutralizingthe lsolution is` effectedby bubbling'CO2 gas through the solution.

'6. The recovery' by the method'of `claim 4 `of the', gallium content:presentin the cycled liquors of the Bayer Process for the Purication VofBau'Xite.

7.. .A 1:1rocedure for the recovery of the gallium content of the anodicmetal produced in the elec-V trolytic refining of aluminum, `whichcomprises dissolving the anodc, metalI in a caustic alkali, removingfrom the solution the undissolved impurities therein, and thenextracting the gallium content of the solution by the methodv of claim4.

8. In a continuously operated system for the treatment of 'an aluminateliquor containing Ya small amount of GazOa vand of sufficiently 10WAconcentration in A1203 to be stable, the method of separating andrecovering its gallium content according. to which the liquor to betreated is delivered at one end of zthe system, partially carbonated atan intermediate point in the system to precipitate as hydroxids most ofvits aluminum content together withsome of its gallium content, this'precipitate removed and redissolved in the liquor entering the' system,the liquor containing this redissolved precipitate treated toprecipitate therefrom substantially pure aluminum hydroxid, this secondprecipitate removed from the system,

the ltrate fromY this Ysecond precipitate partiallyy carbonated at; saidintermediate point in the systemV andthe precipitate so formedredissolved in the liquor entering 'the system, all the residual liquorleft after .the foregoing operations then completely lcarbonated toprecipitate together as hydroXids 'its remaining aluminum content. andgallium content, and the last .named hydroxids removed and'treated rtoseparate and recover theirgallium content.

9; The method of claim 8 in which said second precipitate isfobtafinedby hydrolysis.

10. The method of 'claim 8 in which said sec"- ond precipitate isobtained by treatment with. CO2 added `in small increments.

1'1- The.V recovery by the method of claim 8 of the gallium contentpresent in the cycled liquors o' ythe Bayer Process for the Puricationof Bauxite.

MAURICE BEJA.

REFERENCES' CITED The following references are of record 'in the fileofthis patent:

UNITED STATES PATENTS Number Name Date 382,505 Bayer May 8*, 1888663,167 Hall Dec. 4, 1900= 941,799 McCulloch Nov. 30, 1909 1,013,022Kendall Dec. 26, 19-11 OTHER REFERENCES! Mellor: Comprehensive Treatiseon Inorganic and Theoretical Chemistry, vol. 5, page 376.

Tsvetnye Metally (U. S. S. RJ, 1940, No. 12, pages -64.

Certificate of Correction Patent No. 2,574,008 November 6, 1951 MAURICEBEJA It is hereby certified that error appears in the printedspecification of the above numbered patent requiringr correction asfollows:

Column 3, line 31, strike out precipitation of aluminum hydroxd. Such1'11; and that the said Letters Patent should be read as correctedabove, so that the same may conform to the record of the case in thePatent Ofice.

Signed and sealed this 5th dey of February, A. D. 1952.

THOMAS F. MURPHY,

Assistant O'onmz'asz'mzer of Patents.

1. GIVEN A CAUSTIC ALKALI SOLUTION OF ALUMINOUS MATERIAL CONTAINING ASMALL AMOUNT OF GALLIUM AND OF SUFFICIENTLY HIGH CONCENTRATION IN AL2O3TO BE UNSTABLE, THE METHOD OF SEPARATING AND RECOVERING THE GALLIUMCONTENT THEREOF WHICH COMPRISES FIRST PRECIPITATING BY HYDROLYSIS ANDREMOVING FROM THE SOLUTION SUBSTANTIALLY PURE ALUMINUM HYDROXID TOREDUCE ITS CONCENTRATION IN AL2O3, PARTIALLY NEUTRALIZING THE SOLUTIONBY AN ACID ADDED THERETO IN SMALL INCREMENTS TO SLOWLY PRECIPITATEFURTHER ALUMINUM HYDROXID, REMOVING THIS SECOND PRECIPITATE FROM THESOLUTION, THEREAFTER ACIDIFYING THE SOLUTION SUFFICIENTLY TO CAUSESUBSTANTIALLY ALL OF THE ALUMINUM AND GALLIUM CONTENT REMAINING IN THESOLUTION TO PRECIPITATE TOGETHER AS HYDROXIDS, REMOVING THE LATTERHYDROXIDS AND TREATING THEM TO RECOVER THEIR GALLUM CONTENT.